The present invention concerns a transfer element, in particular a sprue bush or a machine nozzle, for an injection molding system, having a flow lumen for a plasticised plastic material.
The invention further concerns a hot runner system having a sprue bush and an injection molding machine having a machine nozzle.
A sprue system or runner is the connection from the machine nozzle of an injection molding machine to what is referred to as the ingate. The ingate forms the transition from the sprue runner into the mold portion cavity configuration, referred to as the mold cavity. The state of the art discloses hot runner systems for injection molding machines. Such hot runner systems represent the technologically most developed sprue systems or runners for injection molding molds. Hot runner systems serve to distribute the plastic material which is prepared in the injection molding machine in a molten state from the machine nozzle of the injection molding machine to the individual cavities in the injection molding tool. In that respect the hot runner system is temperature-controlled in such a way that the plastic material is kept in the molten state throughout the entire injection molding cycle in the hot runner system. Therefore hot runner systems are frequently also considered as a prolongation of the machine nozzle.
A certain amount of gas is produced during the processing process, during melting and plasticization of plastic materials, in particular PET materials. Presumably the gas contains predominantly substances which are due to additives added to the initial PET material to specifically alter the properties thereof. In that case the gas is produced in particular upon aggregate conversion of the molten material during plasticization by a machine screw by virtue of shearing, heat and overheating, the gas condensing at cooler locations in the injection molding system in the form of dust. That dust is aggressive to a high degree and is deposited in particular at colder parts of the hot runner system. In that case deposit of the dust, in particular in the plunger housings of the needle valves which seal off the hot runner system in relation to the injection molding tool, leads to severe wear of the plunger seals. Therefore many needle valve systems for hot runner systems have vent openings by way of which the dust can escape from the hot runner system before it is deposited in the region of moving parts, for example at the plunger housings of the needle valves, and there gives rise to increased wear.
The amount of dust in the injection molding system increases with the material throughput through the system, that is to say the plasticised amount of plastic material per unit of time. Modern injection molding systems are designed for an increasingly higher level of material throughput which is required in particular by virtue of the increase in the number of mold cavities or molding spaces in the injection molding tools and due to a reduction in the cycle times. Wear in particular in the plunger housings of the valves of the hot runner plate also increases therewith as the increased amount of dust can no longer adequately escape from the system through the vent bores in the plunger housings of the valves.